The surface curvature is of critical importance to the performance of most optical devices. For instance, the focal plane of a curved mirror is determined by the mirror curvature and a refractive lens derives its ability to converge or diverge light from the difference in the curvature of the front and the rear surface. Singly curved optical devices have a surface presenting a curvature in one direction along the surface. Doubly curved optical devices have a surface presenting a curvature in all directions along the surface. Non-exclusive examples of curved optical devices are visors, goggles, rear view mirrors, automotive windows, skylights and headlamps.
In many of these examples, electrochromic devices are of interest for achieving a controllable color and/or transmission. A typical electrochromic device comprises five superimposed layers deposited on one substrate or positioned between two substrates in a joined together configuration. The central part of the five-layer electrochromic stack is an ion conductor (electrolyte). The ion conductor is in contact with an electrochromic film, capable of conducting electrons as well as ions. On the other side of the ion conductor is an electron and ion conducting counter electrode film serving as an ion storage layer. The central three-layer structure is positioned between electron conducting layers. Such a device is colored/bleached by applying an external voltage pulse between the electron conducting layers on the two sides of the stack, causing the electrons and ions to move between the electrochromic layer and the counter electrode layer.
Applications of electrochromic devices include architectural windows, information displays, light filters and modulators, rear-view mirrors, sunroofs and windows in vehicles, eyewear, helmet visors, ski goggles, surfaces with variable thermal emissivity or camouflage. Many of these applications present doubly curved surfaces.
Historically, the first electrochromic coatings were deposited on glass substrates. The possibility of using plastic substrates is described, for example, in WO9923528. Electrochromic devices on plastic substrates are characterized by their light weight, flexibility, and the ease of cutting to complex shapes.
The principal prior art sequence of producing curved electrochromic devices comprises the following steps. It starts with provision of two complementary substrates. The substrates are preformed into a permanent curved shape. Both substrates are coated with electron conducting layers, one substrate is coated with an electrochromic layer and the other substrate is coated with a counter electrode layer. Additional layers, such as bus bars, may also be included in the stack. The two matching substrates are laminated with an electrolyte between them to form an electrochromic device. Finally the edges are sealed.
There are many prior art disclosures presenting different types of doubly curved electrochromic devices. Just a few examples will be presented here. The U.S. Pat. No. 5,953,150 discloses a method for producing doubly curved electrochromic devices for eyeglass lenses. Two half cells, one concave and one convex, are put together with an ion-conducting polymer between.
The published US patent application 2004/0253401 discloses a method of making a curved electrochromic device for portable electronic devices. A compound curved shaped housing part includes integrated activatable electrochromic indicia. The indicia are formed by coating an internal surface of a transparent plastic shell with a sequence of layers including: optionally a separate transparent conductor, an electrochromic material layer, an electrolyte layer, optionally a separate ion donor layer, optionally an insulator layer and a second conductive layer. The electrochromic material is deposited onto pre-curved substrates.
In the U.S. Pat. No. 5,805,367 a transparent electrode formed by an ITO film, an EC layer of an optoelectronic comprising element, a reflecting film also serving as an electrode thin film and an insulating sealing film are deposited on a rear surface of a transparent substrate of a main member of a mirror. The transparent substrate has dividing lines for dividing a mirror surface area into a main mirror surface area of a certain curvature convex surface having a large radius curvature and a supplemental mirror surface area of a gradually varied curvature convex surface having a gradually decreased radius curvature.